When Sen. Mark Pryor (D-Ark.) sought reelection in 2008, he had the luxury of no Republican opponent. Part of the reason he got a pass was the state's long, proud history of moderate and conservative Democrats. And for a moderate-to-conservative Democrat like Pryor, that made him tough to beat.

Six years later, those conservative Democrats are looking more like an endangered species than Pryor's ace in the hole.

According to data from Gallup, the percentage of Arkansans who identify as conservative Democrats has dropped from 15 percent six years ago to 9 percent today.

That might not sound like a huge shift, but look at it this way: In 2008, nearly half of Arkansas voters -- 47 percent -- identified as Democrats. That number is down to 40 percent today, and it's because those conservative Democrats left.

A similar shift is happening in North Carolina; Gallup also recently crunched the numbers there and found a significant drop in people who identify as Democrats. In 2008, when Sen. Kay Hagan (D-N.C.) was first elected, North Carolinians identified with or leaned toward Democrats by a 49 percent-to-39 percent margin. Today, it's just a one-point margin, 42 to 41.

So in both states, nearly half of people in 2008 had some kind of affiliation or affinity with the Democratic Party. And in both states, that number has slid seven percentage points since then.

The question from there is whether that makes these voters less apt to vote for someone like Hagan or Pryor than they were in 2008. Are the electorates they face really that much more difficult than they were back then?

Maybe not. Most of the defectors appear to have become independents rather than Republicans, which means they have essentially moved into the "free agent" column. That's not as good for Democrats as if they were still on the blue team, but it does mean that their votes are attainable for the right kind of Democrat. (Hence all the distancing oneself from President Obama by such Democrats.)

What's most interesting about the numbers above is that even as conservative and/or moderate Democrats appear to be leaving the party in these two states, the trend nationally isn't as sharp.

In fact, the percentage of Democrats who self-identify as conservative is down just two points from 2008 -- from 21 percent to 19 percent. But over the long-term, it's clear where the trend is heading, and fewer and fewer conservatives are sticking with the Democratic Party.

The trendline, it appears, is a bit sharper in some Southern states -- which just happen to be holding key Senate contests this year.